Well, thank you my dear friend for this very interesting question! In asking about the legality of Peter carrying a sword, I do have a couple of thoughts, though these will be mostly from a historical perspective rather than from the Scriptures. From what I understand from Roman history, the citizens of any occupied country, such as Israel, would not typically have been allowed to carry weapons such as swords, unless the people in question were actual Roman citizens (and this would generally not have been the case for native Israelites who were born within the borders of Israel). Peter was not a Roman citizen, so I assume it would not have been acceptable under Roman law for him to have an offensive weapon like a combat sword.  But, was this an actual sword? I think that we have to consider what the word “sword” actually referred to in the passages related to Luke 22 and John 18. As I understand it, the Greek word for “sword” in the passages we are considering, would indicate something more akin to a long fisherman’s knife, and not so much a weapon of combat.  If this last was the case, then Peter’s “sword” would not likely have been illegal under Roman law. I personally doubt in any case that such a law would have been enforced by Roman officials unless it appeared that an actual insurrection was being planned. In addition to this, those who came to arrest the Lord were the temple guards (John 18:3).  These armed men were commissioned by the elders and high priest, and thus, Roman soldiers would not have taken such orders from members of the Sanhedrin, or so I believe. The primary purpose of these men would have been to arrest Jesus, and not so much to be concerned about whether His disciples possessed illegal items.

But now, the first part of your question is one that many have asked, so let’s look to the Scriptures. If we look at Luke 22:31-38; 50-51, we read about the interaction between the Lord Jesus and Peter, that Satan wanted to sift him as wheat, but the Lord had prayed for him that his faith fail not, and that when Peter was restored, he might strengthen his brethren (Luke 22:31-32). To this, Peter responded in verse 33: “…Lord, I am ready to go with Thee, both into prison, and to death.” To this statement, The Lord Jesus responded by foretelling about Peter’s denial (verse 34), then went on to say the following in verses 35-38: “…When I sent you without purse, and scrip, and shoes, lacked ye any thing? And they said, Nothing. Then said He unto them, But now, he that hath a purse, let him take it, and likewise his scrip: and he that hath no sword, let him sell his garment, and buy one. For I say unto you, that this that is written must yet be accomplished in Me, And He was reckoned among the transgressors: for the things concerning Me have an end. And they said, Lord, behold, here are two swords. And he said unto them, It is enough.”

My dear friend, I believe that in the verses I have just cited, we can obtain some insight into why Peter brought his sword (or perhaps his fisherman’s knife) with him to Gethsemane. I believe that Peter failed to understand the Lord’s meaning when He spoke of the time to purchase a sword. Perhaps Peter thought that he and the disciples would need to protect the Lord from the Jews. So, what did the Lord Jesus really mean to impart to His disciples in verses 35-38?  J. N. Darby in his Synopsis of the Bible summarizes this section well: “Jesus then takes occasion to forewarn them that all was about to change. During His presence here below…He had sheltered them from all difficulties; when He sent them throughout Israel, they had lacked nothing. But now (for the kingdom was not yet coming in power) they would be, like Himself, exposed to contempt and violence. Humanly speaking, they would have to take care of themselves. Peter, ever forward, taking the words of Christ literally, was permitted to lay bare his thoughts by exhibiting two swords. The Lord stops him by a word that showed him it was of no use to go farther.  Pressed in spirit by that which was coming, He exhorts His disciples to pray, that they enter not into temptation…” My conclusion from all of this is that the Lord was foretelling what was about to happen: the arrest of Jesus, the trial and the crucifixion, and that the disciples would soon encounter much persecution. I think that Peter erroneously took the Lord’s message to be that he would need a sword, and his particular mindset might have been to protect his Lord and perhaps himself with a weapon. But this was not at all the Lord’s meaning, so when Peter tried to use his sword, the Lord stopped him, ”Then said Jesus unto him, Put up again thy sword into his place: for all they that take the sword shall perish with the sword. Thinkest thou that I cannot now pray to My Father, and He shall presently give Me more than twelve legions of angels? But how then shall the scriptures be fulfilled, that thus it must be?” (Matthew 26:52-54). The Lord Jesus didn’t need or desire Peter and the disciples to defend Him. Peter may have thought that he could help by defending the Lord with his weapon; however, the Lord pointed out in verse 54 that the Scriptures must be fulfilled…Christ Jesus must go to the cross for poor, ruined sinners like you and me, or else we could never be saved. Peter’s intentions with his sword thus demonstrated his total lack of understanding of God’s purposes for Christ. In John 18:4 we read: “Jesus therefore, knowing all things that should come upon Him, went forth….” Praise God for that blessed One who gave Himself for us! The Lord Jesus came into this world to save sinners (1 Timothy 1:15; John 3:16; 1 John 4:10), and this being God’s plan for salvation, it could not be interfered with through man’s fleshly reasoning and efforts.  (SF)  (611.2)